Spindle assemblies used in machine tools for machining wood, plastic and nonferrous materials typically include a housing mounted on a vertically displaceable toolhead support assembly, a pair spaced roller bearings mounted in the housing and a spindle journaled in the bearings. The outer races of the bearings usually are seated in bearing seats machined in the ends of the spindle housing. Drive is transmitted to the spindle by means of a belt drive connected to a lower depending portion of the spindle. Such spindles generally are operated at speeds in the range of 10,000 to 20,000 rpm.
In such assemblies, it has been found that if the bearing seats are not precisely concentric so that the spindle is coaxial with the bearings, laterally directed loads produced by the high speed rotation of the spindle will create an axis of inertia that is nonparallel to the axis of rotation of the spindle, resulting in undue wear of the bearing seats, the bearing roller balls and/or the spindle. Such condition ultimately leads to malfunctioning and often failure of the assembly.
Such problem in spindle assemblies has been addressed and largely overcome by the solution described and claimed in U.S. Pat. No. 5,305,525. The solution provided there consists of forming a pair of bearing seats in the spindle housing slightly oversized relative to the outer dimensions of the bearings, mounting a first bearing on the spindle, applying an adhesive bonding material on the outer race of the first bearing and a first bearing seat in the spindle housing, inserting the spindle with the first bearing mounted thereon into the housing so that the outer race of the first bearing is seated on the first bearing seat, applying an adhesive bonding material to the second bearing seat and the outer race of the second bearing, mounting the second bearing on the other end of the spindle while inserting the second bearing in the second bearing seat and then allowing the bonding materials to set, assuring an axial alignment of the spindle and bearings.
The procedure of aligning the spindle with the bearings and then securing the outer races of the bearings in their respective bearing seats in the spindle housing has greatly improved the operation and longevity of the spindle and bearings in such assemblies. It further has been found, however, that such assembly procedure and resulting construction providing for an accurate alignment of the spindle and bearings has not provided for the axial displacement of the spindle within the spindle housing, normally caused by heat developed in the operation of the spindle at considerably high speeds. It thus has been found to be desirable to provide a spindle assembly of the type described which not only provides for a proper alignment of the spindle and the bearings but further allows for the axial displacement of the spindle relative to the spindle housing when the spindle is rotating at high speeds.